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gain increase using negative resistance circuit

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sharkies

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often cascoding is used to increase the gain of your circuit.
The same can be achieved by using negative resistance circuit.
However, I haven't seen wide use of them. It seems like with good design of negative resistance circuit you can achieve high gain in low supply voltage cmos processes. But I haven't seen many examples in opamps yet... Y is this so?
 

negative resistor should be used in combination with positive resistor to achieve high gain. it is often used, or example, in high gain comparator design.
 
sharkies said:
often cascoding is used to increase the gain of your circuit.
The same can be achieved by using negative resistance circuit.
However, I haven't seen wide use of them. It seems like with good design of negative resistance circuit you can achieve high gain in low supply voltage cmos processes. But I haven't seen many examples in opamps yet... Y is this so?
Click to expand...

I suppose, you have seen already several design solutions based on current sources instead of resistors. Now, realize that a negative resistance is nothing else than a voltage controlled current source. For specific applications, the negative resistance can be made frequency dependent.
 
LvW said:
I suppose, you have seen already several design solutions based on current sources instead of resistors. Now, realize that a negative resistance is nothing else than a voltage controlled current source. For specific applications, the negative resistance can be made frequency dependent.
Click to expand...

yep, negative resistance is easily controlled through the current, it is often used in oscillators, RF VOCs and in wide band amplifiers.
 
As mentioned by others, negative resistance is essentially a vccs. It commonly comes in the form of cross-coupled circuits. It uses positive feedback and hence often used for hysteresis comparators, latches and oscillators.

You may have seen papers where it is used with a diode (ie positive resistor) to achieve a zero small-signal transconductance load. I read somewhere that it even has a name, called a Lee Load.

The problem comes in when you have to guarantee that the positive feedback does not dominate under all corners and monte-carlo distributions. Otherwise, you'll be dealing with stability and lockout issues.
 
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